1. Field of the Invention
The present invention relates to a stacked PTC thermistor and to a process for its production.
2. Related Background Art
PTC (Positive Temperature Coefficient) thermistors are known as thermistors with positive resistance temperature characteristics, whereby the resistance increases with increased temperature. PTC thermistors are utilized in self-regulating heating units, overcurrent protection elements, temperature sensors and the like. As such PTC thermistors, there have conventionally been implemented single-layer PTC thermistors comprising a semiconductor ceramic layer with conductivity imparted by adding a trace amount of a rare earth element to barium titanate (BaTiO3) as the main component, and a pair of external electrodes sandwiching the semiconductor ceramic layer.
In recent years, demand has sharply increased for PTC thermistors with sufficiently low resistivity at ordinary temperature during non-operating periods (hereinafter referred to as “room temperature resistivity” for convenience), in order to reduce power consumption. Since the room temperature resistance of a PTC thermistor is inversely proportional to the electrode area, a larger electrode area can lower the room temperature resistance. Stacked PTC thermistors obtained by alternating lamination of multiple semiconductor ceramic layers and multiple internal electrodes have been proposed as alternatives to conventional single-layer PTC thermistors. In stacked PTC thermistors, lamination of multiple internal electrodes can drastically increase the electrode area and thus reduce the room temperature resistance.
An example of a stacked PTC thermistor is disclosed in Japanese Patent Publication No. 3636075. This stacked PTC thermistor has an electronic part body obtained by alternating lamination of a barium titanate-based semiconductor ceramic layer and a base metal internal electrode, and an external electrode formed at the edge face of the electronic part body. The stacked PTC thermistor is formed by impregnating the electronic part body with a glass component. In Japanese Patent Publication No. 3636075, the stacked PTC thermistor is indicated as having low resistance and a high withstand voltage.